1. Field of the Invention
The present invention relates to a photometric device provided for a camera or the like, and more particularly to a photometric device capable of determining a backlight situation.
2. Description of the Related Art
In recent years, cameras capable of partial photometry or spot photometry have become widely used, in which luminance is measured in a specific portion of a photographic area and photographs are taken on the basis of the information on the luminance. Since these cameras faithfully reproduce brightness of a portion which a photographer wishes to shoot, they are considerably effective especially when a subject is small or when a great difference exists in luminance between a subject and its surroundings.
Another proposed technique is to measure luminance in a central portion and a peripheral portion of a picture, determine from the difference between them that a scene to be photographed is a backlighted scene when the central portion is dark and the peripheral portion is bright, and correct exposure or take photographs with an electronic flash. This technique can prevent underexposure for a person or a subject in the central portion resulting from a photograph taken with reference to brightness of the overall picture.
Japanese Patent Laid-open No. 57-122421 has proposed a technique of manually changing a ratio of combined outputs of spot photometry for measuring subject luminance in a central portion of a picture and peripheral photometry for measuring luminance in a peripheral portion. With this technique, real time photometry for shutter opening can be performed as intended by a photographer.
Japanese Patent Laid-open No. 61-91524 has proposed a photometric device for detecting a backlight situation by using a difference in output between partial photometry and averaging photometry, in which an area for partial photometry is set to include a portion below the center of a picture. In addition, Japanese Patent Laid-open No. 60-213931 has proposed a technique of performing distance measurement and photometry in a plurality of areas to determine a backlight situation based on a combination of a plurality of the distance and luminance information.
When it is determined whether a subject is backlighted or not, the determination is most readily made if the subject extends over all the area where photometry is performed and its surrounding area where peripheral photometry is performed does not include the subject. To achieve this, an area where photometry is performed is preferably a smaller spot so that the situation of a subject may be more appropriately supported.
As shown in FIG. 10, however, when a photometric sensor performs photometry in a smaller spot (shown by a line “output from photometric sensor for small area” in FIG. 10), a wide dynamic range cannot be ensured, thereby presenting a contradictory problem that the sensor fails to produce an output at a lower luminance, and thereby fails to accurately perform photometry.
As a solution to the problem, the photometric device proposed in Japanese Patent Laid-open No. 61-91524 is designed to have an area for partial photometry including a portion below the center of a picture since a subject is likely to exist in a lower portion of the picture.
In this case, however, the area for partial photometry cannot also be reduced in size in order to allow photometry at a lower luminance in the area for partial photometry. In addition, for an extremely small subject, photometry is performed in an area including a portion other than the subject even when the subject exists in the center. It is thus impossible to accurately detect backlight.
The photometric device proposed in Japanese Patent Laid-open No. 60-213931 performs distance measurement and photometry in a plurality of areas to determine a backlight situation based on a combination of a plurality of the distance and luminance information. In this case, when the plurality of areas serving as photometric areas have a large size, no problem occurs if a subject extends over all the photometric areas, but if a subject extends only over some of the photometric areas, accurate backlight detection is difficult to perform.